<VV> Carb cut out question - Corvair Buggy

[grant young]

I have been working with a Corvair dune buggy owner to try to resolve a
carb cutout problem he has. We have rebuilt his carbs, installed .053" main
jets, and installed .110" ball valve fuel inlets in the LM carbs. He says
that when he goes over severe bumps the engine cuts out and eventually
dies, as if flooding. He says that turning OFF the auxillary electric fuel
pump helps the situation. I saw a picture of the carbs, and they are
completely covered in sand/dirt, probably from fuel getting on the outside
of them (since the rest of the engine is clean, it is probably not a oil
leak). He is going to install vent tubes in the tops and lower the float
level 1/8" to see if that helps. I am wondering if there is another buggy
owner out there who has experienced the same thing, or if anyone has any
advise. 
Thanks,
The (tripod) Carbmeister